The present invention does not relate to oil-based clays comprising naturally occurring clays that are mined as rocks. Rather, the present invention relates to man-made, water-based modeling doughs.
Non oil-based modeling doughs are normally air-dryable and incorporate starch as the filler. These doughs have a tendency to flake, crack, and crumble in both the wet and dry stages. These doughs also shrink substantially upon drying. In other words, these doughs are characterized by poor plasticity, poor dry strength and substantial drying shrinkage.
Plasticity is the property of a wet dough or clay that permits deformation by application of a relatively slight pressure and retention of the deformed shape after release of the pressure. This property distinguishes the dough in its wet stage from its dry stage. When wet, starch-based modeling doughs have a low plasticity and have a tendency to break apart during the molding or manipulating process. These doughs also have a tendency to crack when dry and are not easily shaped in the dry state by sanding or filing. Furthermore, the artist cannot easily add wet dough to the existing dried sculpture. Finally, artists cannot carve dried starch-based doughs.
Another problem inherent with water-based doughs is the loss of volume (shrinkage) upon drying. Because water accounts for a large portion of the volume of the dough in its wet stage, water loss upon drying results in a loss of volume in the resulting molded product.
One attempt to overcome the shrinkage problem has been to incorporate large proportions of filler in the dough mixture, but there is still shrinkage because the volume decreases as the filler binds together after drying. One commercially available children's dough, for example, shrinks about 20% upon drying despite its high filler content. In other words, a sculpture made with that dough can lose about 20% of its total volume upon drying. Moreover, the use of large proportions of filler aggravates the flaking, cracking and crumbling problem discussed above, and also tends to decrease the dry strength of the molded sculpture.
Discoloration upon drying is another problem associated with water-based doughs and is compounded by the dry shrinkage discussed above. As the volume decreases, the concentration of the pigment increases and the color darkens.
Yet another problem associated with conventional water-based doughs is that they are heavy and hard to manipulate. Dense, heavy doughs are awkward and the child or artist is limited in the types of shapes that can be created without the dough falling apart.
Finally, currently available water-based doughs are destructive to textiles, carpeting, furniture and other surfaces. They tend to stain a surface and are not easily removed by washing.
In light of the above problems, the need arises for a water-based air-drying dough that is easily washed from textiles, carpeting and other surfaces. Furthermore, the water-based, air-drying dough must be able to incorporate dyes and pigments and not discolor upon drying.